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1 Job stress bio-monitoring methods: heart rate variability (HRV) and the autonomic response Jesper Kristiansen Objectives After the presentation you will: Know what heart rate variability is and how it is measured. Have a basic understanding of the physiology behind HRV. Understand how HRV is related to activity in the parasympathetic and sympathetic branches of the autonomic nervous system. Know of different ways to apply HRV measurements in research. 1

10 Summary so far Beat-to-beat variability in HR ( instantaneous heart rate) is governed by modulations in SNS and PNS activity. Due to the dependency of a 2nd messenger system the modulations of SNS activity has lower maximum frequency than PNS modulations. Hence, an analysis of the frequency content of HRV will reveal the contributions from PNS (high frequency modulations of instantaneous HR) and SNS (slow frequency modulations). 2. Analysis of HRV 10

18 10s fluctuations in HR Oscillations caused by resonance between HR and different blood pressure regulating systems, e.g.: baroreceptor reflex renin-angiotensin system local endothelial NO system Afferent nerve signal from these blood pressure regulating systems are integrated in the CNS. The HR is result of the balance between efferent nerve traffic from sympathetic and parasympathetic nerves (sympatho-vagal balance). Frequency domain measures HF spectral power is modulated by parasympathetic activity only LF spectral power is modulated by both sympathetic and parasympathetic activity LF/HF reflects sympathovagal balance. 18

19 Summary: HRV measures HRV is derived from analysis of (normal) R-R intervals, e.g., recorded from an ECG HR oscillates with many frequencies (complex pattern in tachogram) that reflects the influence of different blood pressure systems Rapid fluctuations (HF, Hz) is caused by vagal activity Slow fluctuations (LF, Hz) is caused by a mixture of sympathetic and vagal activity. Slower fluctations is caused by even slower regulatory systems (e.g., temperature fluctations, day-night periodicity). 4. Factors that influence HRV 19

21 Physical exercise and HRV Regulation of HR during exercise depends on: Size of the active muscle mass Type of exercise (single bout, repeated, static vs. dynamic) Intensity of the exercise Body position during exercise. HRV and gender Low frequency components of HRV are lower, and high frequency components higher, in women compared men Crude and adjusted mean values (± SD) of LF, HF and total power in men and women. Kuch et al., (2001). Determinants of short-term heart rate variability in the general population. Cardiol 95:

22 HRV and HR, age LF and HF decrease with HR and age Regression coefficients (b) and partial R2 values of factors related to LF and HF power in forward stepwise regression model Kuch et al., (2001). Determinants of short-term heart rate variability in the general population. Cardiol 95: HRV has a diurnal rhythm Low frequency components of HRV are lower, and high frequency components higher, at night compared to day Raemaker et al. (1998). Heart rate variability and heart rate in health volunteers. Eur Heart J 19:

31 Work stress and HRV Notes on the HRV measurements: Ambulatory ECG recordings performed on 109 men. RMSSD used to assess vagal tone at work, leisure time, and sleep. Diary information used to code for body posture and activity. Work stress and autonomic regulation Am J Ind Med 2005; 48:

32 Work stress and autonomic regulation HF higher in subjects with low job strain 500 Mean High Frequency Power Awake Sleep After Dinner Before Dinner Afternoon on Rest Da Lunch Morning on Rest Day Awake on Rest Day Sleep Job Strain Low After Dinner Before Dinner Afternoon at Work Lunch Morning at Work 100 High Sociological Period HRV and work-related stress Sympathetic indices (incl. LF/HF) increase with strain at work but not with overall strain. 32

33 HRV and work-related stress Notes on the HRV measurements: Ambulatory 48-hours ECG recordings performed on 36 men. Ectopic beats and artifacts removed by manual screening. Spectral components of HRV calculated for 5-min ECG segments (for whole 48-hr recording) Diary information used to control for body posture and exertion. 5. Examples on research applications of HRV: d) Intervention to reduce stress at work 33

35 Stress reduction (intervention) White-collar workers in company during downsizing (n=51). Effect of a stressmanagement program (SMP, n=26) versus sham program (SP=25). Stress reduction (intervention) Notes on the HRV measurements: 5-10 min ECG recordings performed on 170 men at the worksite (workers) or at home or at the clinic (controls). Standing induced changes in HRV used to assess autonomic reactivity. Spectral components of HRV calculated for 5-min ECG segments. 35

36 Summary - I HRV can be applied in both laboratory and field studies. Ambulatory measurements and measurements performed in work places or at home are feasible. HRV can be measured in the awake state or in the sleep. HRV have been applied succesfully in studies of psychosocial factors, including workplace stress. HRV (or certain HRV metrics) are generally accepted as associated with CVD risk. Summary - II Time domain metrics can be used for long-term recordings, frequency domain metrics for short term recordings. Time domain metrics more robust to the influence of ectopic beats, pauses, artifacts,etc., but are more difficult to interpret physiologically. Frequency domain HRV metrics can be interpreted physiologically, but ECG needs careful screening before analysis. 36

37 Summary - III HRV (and derived metrics) are extremely sensitive to Body posture Mental activity HRV (and derived metrics) also depends on Age, BMI, sex, physical fitness, and other lifestyle factors It is advisable to address the effects of these variables in the study design Thank you for your attention! 37

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